What does this JavaScript snippet output?

1const it = {
2  data: [1, 2, 3],
3  pos: 0,
4  next() { return this.pos < this.data.length ? { value: this.data[this.pos++], done: false } : { value: undefined, done: true }; },
5  [Symbol.iterator]() { return this; },
6};
7let sum = 0;
8for (const n of it) sum += n;
9console.log(sum);